This message appears to be false, as both virtual machines have AMD-V disabled.

The only option which has been set under "Settings > General > Advanced > Extended Features" is "Enable ACPI", all others (including "Enable VT-x/AMD-V") are unchecked.

With AMD-V enabled in both virtual machines, I am able to load both simultaneously. This is opposite behaviour as compared to VirtualBox 2.0.6, wherein I was *unable* to load the second virtual machine with AMD-V enabled, receiving the same message as above: